1. Field of the Invention
The present invention relates to etching or coating plants for purely physical processes and also for plasma supported chemical processes PECVD as well, having a vacuum recipient and a pair of electrodes located at a distance from each other and adapted to capacitively produce an AC-plasma discharge in the recipient; it relates further to a method of igniting plasma discharges and to a method of intermittently operating same.
2. Description of the Prior Art
Sputtering plants of the mentioned kind or of a similar kind are disclosed in the following patent documents: DE-OS 1 790 178, DE-OS 2 022 957, DE-OS 3 706 698, EP-A-0 271 341, U.S. Pat. Nos. 4,572,759, 4,278,528, 4,632,719, 4,657,619, 4,132,613, 4,557,819, 4,466,872, 4,552,639, 4,581,118, 4,166,018, GB-A-1 587 566, 1 569 117, 1 358 411, 1 111 910, 1 258 301, 2 157 715. It is, thereby, a general procedure to either operate both electrodes for the capacitive excitation of the plasma such as for instance disclosed in EP-A-0 271 341 electrically through insulating feed-through entrances through the wall of the recipient or to use merely one of the electrodes this way and the entire wall of the recipient as a second electrode, for instance and specifically to connect it as an "anode" to ground.
With regard to the physics of the so-called AC- or especially Rf-sputtering technique attention is drawn to H. R. Koenig and L. I. Maissel, IBM J. Res. Develop. 14, Mar. 1970, p. 168, further to the technical publication BB 800 015 DD (8404) of the Balzers Company, K. Hoefler and K. Wellerdieck, and to the thesis of K. Wellerdieck "Die Potentialverteilung in Hochfrequenz-Gasentladung der Zerstaubungstechnik" (The distribution of the potential in the Rf-gas discharge of the sputtering technique), 1988, University of Karlsruhe.
The procedures which have been used up to now, namely to operate either both electrodes or also only one which is electrically insulated from the wall structure of the recipient, via feed-through entrances through the wall structure of the recipient feature the following drawbacks:
They cause the necessity of providing at least one vacuum tight insulating feed-through through the wall structure of the recipient. Furthermore, the at least one electrode set off from the wall structure of the recipient blocks a relatively large part of the process space and, therefore, the recipient is relatively voluminous.
If the electrical supply of one of the electrodes is fed vacuum tight and insulated through the wall structure of the recipient and this wall is operated in its entirety as a second electrode, e.g. connected to earth potential, the design regarding the selection of the ratio of the surfaces of the electrodes which face towards the inner side of the recipient is extremely curtailed. Usually, the electrode which then is formed by the complete wall structure of the recipient is regarding its surface substantially larger than such of the electrode with the feed-through through the wall structure.
Since a workpiece to be etched must be located at the smaller one of the electrodes (surface/voltage law of Koenig), thus, in this case at the mentioned electrode with the feed-through, and since generally AC-potential is applied to this electrode and not to the housing of the recipient or the wall structure of the recipient, it is necessary to apply in this case the workpiece to be etched on an electric potential. Thereby, it rests not only on an AC-potential, because it is this smaller electrode which, due to the discharge, develops also a DC-potential (self-bias potential). A workpiece connected to voltage (on the smaller electrode with feed-through, wall of recipient connected to reference potential) is substantially more cumbersome regarding any kind of automatic handling.
In summarizing it therefore can be stated that an electrode located in the inside of the recipient, separated locally from the wall of the recipient and operated electrically insulated from aforementioned wall, occupies space which must be considered when designing the recipient, necessitates further a vacuum tight lead-in or feed-through through the wall of the recipient, and that finally by such an electrode the flexibility regarding the allocations of large/small surfaces of the electrodes (Koenig) reference potential/DC-floating potential are curtailed.